The invention is generally related to functionally testing an electrical connector, and in particular, to testing a digital data bus electrical connector for reliability.
Many systems and networks of systems rely upon the communication of digital data along electrical transmission lines. The digital data has a predetermined data rate during which an electrical signal composed of pulses selectively varies between high and low voltage levels. These transmission lines interconnect all levels of electronics from integrated circuit, module, system, and network. Even systems that convey digital data in a radiant form of energy such as visible light in a fiber or radio frequency (RF) broadcast still depend in part on electrical transmission lines for a portion of the communication.
Typically, an electrical signal has clearly defined rising and falling edges that must transition within a predetermined amount of time for correct reception. Often, the electrical signal is clocked such that a data bit is transmitted at each transition of a clock signal. Failure of the electrical signal to transition from a high voltage level to a low voltage, or the reverse, prior to an associated clock signal transition results in the incorrect digital state (e.g., 1 rather than 0) being received.
The ability of an electrical transmission line to transmit data in a timely manner is often affected by the impedance in the line. Impedance is often considered to incorporate a resistive component and a reactive component, and can result in distortions in an electrical signal that delay signal transitions and potentially create data transmission errors.
Increasingly, higher data rates are used in electrical transmission lines. As such, the time frame that transitions in a signal must be received continues to decrease, making impedance an ever-increasing concern for digital transmission systems. Consequently, distortion of the electrical signal may impose an upper limit on the data rate that may be achieved within a given transmission line.
Certain types of electrical components within an electrical transmission line can affect impedance levels and line reliability. For example, faulty electrical connectors, or interconnects, can often introduce unacceptable impedance levels into an electrical transmission line. The physical mechanism for such unacceptable impedance in an electrical connector may be a reduced conducting surface area between electrical contacts due to variations in manufacturing, contamination, and material wear. With the reduced conducting surface area, the resistive nature of the electrical connector increases. This increase in resistance aggravates any reactive characteristics of the electrical connector. In addition, the reduced coupled surface area may also increase the capacitance of the electrical connector, given the increase in closely spaced, uncoupled surface areas surrounding the coupled surface area.
Because of these variations in electrical connectors, there exists a need for ensuring that an electrical connector will perform reliably in various environments. Reliability testing is often necessary since the variations may be difficult to overcome by other means, such as by choice of electrical connector design. Moreover, an electrical connector design may require validation in a different environment.
It is generally known to estimate reliability of an electrical connector by xe2x80x9cglitch detectingxe2x80x9d, in which a DC voltage is used to measure changes in resistance over time. If an electrical connector has a resistance value that varies more than 10 milli-Ohms (mxcexa9), then a failure is deemed to have occurred, based on a belief that a 10 mxcexa9 variation means that 90% of the contact area has been lost. Reliability testing with a glitch detector is a coarse pass/fail test and not a direct indication of the suitability of an electrical connector to a specific application.
Even assuming that measuring variation in resistance of an electrical connector indicates reliability, generally known glitch detectors are subject to a number of sources of inaccuracy in measuring resistance. As the data rates required of electrical connectors increases, glitch detectors have to measure minute variations in resistance that last for correspondingly shorter periods of time. At these short durations, the resistance measurements are increasingly subject to electromagnetic interference (EMI), and thus cumbersome EMI shielding techniques must be employed.
Consequently, a significant need exists for a testing technique of an electrical connector that indicates whether a desired data rate may be reliably transmitted by the connector.
The invention addresses these and other problems associated with the prior art by providing a test apparatus and method of determining the reliability and/or suitability of an electrical connector for use at a desired data rate by sensing a propagation delay imposed by the electrical connector on a test signal.
In one aspect consistent with the invention, a test apparatus includes a connector interface and a test circuit. The test circuit generates a test signal that is transmitted through an electrical connector via the connector interface. The test circuit determines the reliability of the electrical circuit by determining a propagation delay imposed on the test signal by the electrical connector.
In another aspect consistent with the invention, a method of testing an electrical connector for reliability includes interfacing a test signal path to through the electrical connector, transmitting a test signal along the test signal path through the electrical connector, and detecting a propagation delay in the test signal after it has been transmitted through the electrical connector.